macOS · Storage & Backup
Partition, format, and erase disks
Use Disk Utility to create or resize partitions, format internal or external drives to a specific file system, and erase disks before reuse.
How to open Disk Utility: Partition & Format Drives
- Open Disk Utility from Applications → Utilities
- Select the disk or volume in the sidebar
- Choose Partition, Erase, or First Aid from the toolbar
- Confirm the file system format and apply changes
What you should know
- Located in Applications → Utilities → Disk Utility
- Supports APFS, Mac OS Extended, and exFAT/MS-DOS formats
- Can create multiple partitions or a single-container APFS volume group
- Shows all connected internal and external storage devices
Why it matters
Disk Utility is the primary tool for preparing storage devices for use with a Mac, whether that means formatting a new external drive, reclaiming space by resizing a partition, or fully erasing a drive before selling or repurposing it. Choosing the right file system format directly affects compatibility with Windows, older Macs, and specific use cases like Time Machine or bootable installers. Understanding partitioning also matters for users setting up dual-boot configurations or dedicated backup volumes.
Best practices
- Use APFS for drives used exclusively with modern Macs
- Use exFAT for drives shared between Mac and Windows
- Back up any data on a drive before erasing or repartitioning it
- Choose GUID Partition Map for drives that need to boot a Mac
Common problems and fixes
- A drive isn't recognized by Windows after formatting
- Reformat as exFAT or MS-DOS (FAT) instead of APFS or Mac OS Extended.
- Can't resize a partition
- Ensure no data occupies the space being reclaimed, and that the volume isn't currently in use.
- Erase option is grayed out
- Unmount other volumes using the disk, or boot from Recovery Mode to erase the startup disk.
Tips and tricks
- Use the First Aid tab to verify a drive's health before repartitioning
- Name volumes clearly to avoid confusion when multiple drives are connected
Frequently asked questions
What's the difference between erasing and formatting?
Erasing removes all data and rewrites the file system; formatting refers to the file system type chosen during that process.
Can I undo a partition change?
No, partitioning changes are immediate and data in resized or removed partitions can be lost.
Which format should I choose for a Time Machine backup disk?
APFS or Mac OS Extended (Journaled) are supported; Disk Utility will guide you when setting up the backup.
Related settings
- External StorageExternal Storage covers how macOS handles USB, Thunderbolt, and network-attached drives connected to your Mac — formatting them, choosing a file system, ejecting safely, and deciding which ones are eligible for Time Machine backups. Disk Utility is the main tool for managing these drives.
- Disk Utility First AidRun Disk Utility's First Aid tool to check a disk or volume for directory and file system errors and attempt automatic repair.
More Storage & Backup guides for macOS
- Time Machine BackupTime Machine automatically backs up your entire Mac — apps, accounts, preferences, and files — to an external or network drive, so you can restore individual files or your whole system if something goes wrong.
- Storage ManagementStorage settings show a visual breakdown of exactly what's using space on your Mac's disk, plus built-in recommendations — like storing files in iCloud or automatically emptying the Trash — to free up space without manually hunting for large files yourself.
- Optimize StorageOptimize Storage is a set of Apple-recommended actions — like storing files in iCloud, auto-emptying the Trash, and removing watched TV shows and movies — that free up local disk space with minimal effort. It's found inside About This Mac's Storage settings.
- iCloud DriveiCloud Drive keeps your files in sync across every device signed into the same Apple ID, and can automatically include your Desktop and Documents folders so they're backed up and accessible from any Mac, iPhone, or iPad. Files sync in the background and are accessible from the Finder sidebar or iCloud.com.
- Documents & Desktop iCloud SyncAutomatically upload the contents of your Desktop and Documents folders to iCloud Drive so they stay backed up and accessible from other signed-in devices.
- Migration AssistantMove apps, files, user accounts, and settings from another Mac, a Time Machine backup, or a Windows PC onto your current Mac using the built-in Migration Assistant utility.